AST: __uuidof should leak through templated types

Summary:
__uuidof on templated types should exmaine if any of its template
parameters have a uuid declspec.  If exactly one does, then take it.
Otherwise, issue an appropriate error.

Reviewers: rsmith, thakis, rnk

CC: cfe-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D1419